The rapid automated handling of seedlings has been made possible by developments in the realm of elastomeric soil plugs (hereinafter often referred to simply as "plugs"). U.S. Pat. No. 4,130,072 and the prior art cited therein suggest growing plants within polymerized soil plugs, and by handling the plugs alone, transplanting the plugs. The soil plugs are cast from a slurry of soil and polymer in the form of small, generally cylindrical, resilient objects having a seed-receiving recess formed therein. The plugs are preferably cast in a closely spaced formation in a rectangular tray having slightly tapered cylindrical bores to define the mold cavities. After the plugs have cured in the tray they are seeded, and the seedlings are grown in the tray, typically in a greenhouse. The seedlings are allowed to attain a just sprouted condition prior to planting. The sprouted seedlings are characterized by a foliage end at the upper surface of the tray and a somewhat smaller diameter butt end at the lower surface.
Commonly owned copending application Ser. No. 150,486, filed May 16, 1980, now U.S. Pat. No. 4,355,588, discloses a transplanting machine that rapidly and accurately places plugs into the ground. The transplanting machine described therein makes it possible to achieve a planting rate and crop yield far in excess of those attainable by using prior art methods. In the transplanting machine, plug gripping clips are carried on a planting conveyor, and the plugs are presented to the passing clips on a one-to-one basis for subsequent plug placement in the ground. The above-referenced application discloses the use of a carousel feeder incorporating components of the present invention. The feeder comprises a horizontal conveyor carrying a plurality of serially disposed, closely spaced plug holders, each of which is preferably in the form of a trough. It will be readily appreciated that no matter how much the transplanting machine design is refined, an ultimate upper limit on the planting rate is set by the rate at which plugs may be transferred from the trays to the carousel troughs.
Hand loading of the plugs into plug holders has been found to be a commercially viable option, at least to the point of making the soil plug technology competitive with conventional direct seeding techniques. However, loading plugs in this manner is expensive in terms of labor costs, and the maximum speed at which a worker can load the plugs appears to set a limit on the overall planting rate that is lower than the limit imposed by other considerations.
Commonly owned copending U.S. Patent application Ser. No. 62,667, filed Aug. 1, 1979, now U.S. Pat. No. 4,294,170, is directed to a previous transplanting machine design, and discloses an automated system for repeatedly indexing the trays and ejecting plugs therefrom. Particular apertures of the tray are first indexed to correspondingly spaced apertures in a receiving device that is momentarily stationary with respect to the tray, after which a plunger mechanism is actuated to eject the plugs from the tray into the receiving device. This tray indexing and plug ejection system clearly provides many benefits in the nature of automated plug handling, but is itself not without problems. The system utilizes hydraulic actuation of the ejection pins, thus providing what is in essence a constant velocity motion. In the event that it is desired to speed up the overall operation of the machine, there is a tendency to lose the relative timing of the operations. Additionally, if a tray should happen to be slightly misregistered with respect to the ejection pins, so that the ejection pins impinge on a non-apertured portion of the tray, there is a tendency to cause damage to the tray or the machine. Moreover, the requirement of transferring plugs from the tray to a moving carousel presents some additional problems that are not addressed by the previous system.
A further consideration involves the geometric configuration of the plug loading and feeding apparatus. As discussed in the above-mentioned co-pending applications, it is common practice to plant two rows on each bed, and to plant several beds on each pass. Therefore, if the transplanting machine is to be reasonably compact, the plug loader and feeder must be confined within a relatively narrow space.
Therefore, as the art of transplanting elastomeric soil plugs becomes more and more highly developed, there is presented the need for a machine to automatically and reliably transfer plugs from the trays to the operative plug placement components of plug handling machinery.